Stable Cycling Lithium-Sulfur Solid Batteries with Enhanced Li/Li₁₀GeP₂S₁₂ Solid Electrolyte Interface Stability

Area of Science:

• Materials Science
• Electrochemistry
• Solid-State Batteries

Background:

• Interface instability between solid electrolytes and lithium metal hinders the development of high-performance solid-state batteries.
• Lithium superionic conducting Li$_{10}$GeP$_{2}$S$_{12}$ (LGPS) is a promising solid electrolyte, but its interface with Li metal requires stabilization.
• Achieving stable lithium stripping/plating is crucial for the longevity of lithium-based batteries.

Purpose of the Study:

• To enhance the interface stability between the LGPS solid electrolyte and Li metal using an ionic liquid.
• To investigate the formation of an in situ solid electrolyte interphase (SEI) layer for improved interfacial properties.
• To fabricate and evaluate Li-S solid-state batteries utilizing the modified interface and optimized cathode materials.

Main Methods:

• Employing 1 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI)/ N-methyl- N-propylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR$_{13}$TFSI) ionic liquid as an interface modifier.
• Fabricating Li/LGPS/Li symmetric cells to assess interfacial resistance and Li stripping/plating performance.
• Constructing Li-S solid-state batteries with S@C composite cathodes (S@KBC, S@PBX51C, S@MCNTs) and LGPS solid electrolyte.

Main Results:

• The ionic liquid modifier formed an in situ SEI layer, significantly improving Li/LGPS interface stability.
• Interfacial resistance was reduced from 2021 to 142 Ω cm$^2$, and stable Li stripping/plating was achieved over 1000 hours.
• Li-S batteries with S@Ketjen black carbon (KBC) cathodes exhibited superior discharge capacity (1017 mA h g$^{-1}$) and stability compared to other carbon types.

Conclusions:

• The ionic liquid effectively stabilizes the Li/LGPS interface, enabling robust lithium metal cycling.
• The S@KBC cathode demonstrates excellent performance in Li-S solid-state batteries due to its high surface area and favorable pore structure.
• This approach offers a promising strategy for developing high-performance and stable lithium-sulfur solid-state batteries.